A sterilization apparatus sterilizes objects to be processed accommodated in a processing chamber such as medical tools or food package materials to a high degree. Patent Document 1, for example, shows the use of nitrogen oxide (NOx) gas for the processing of the objects. The sterilization apparatus of Patent Document 1 is an apparatus that uses nitrogen oxide gas for sterilizing coliform bacillus present on food. The nitrogen oxide gas is produced by introducing a gas mixture of nitrogen and oxygen into a plasma generating chamber and turning the gas mixture into plasma.
The sterilization efficiency is not necessarily high with the use of nitrogen oxide gas and there were needs for improvements in the sterilization efficiency. Through vigorous research, the applicants of the present application have found out that it is nitrogen dioxide (NO2), one of various nitrogen oxides (NOx), that substantially contributes to sterilization of bacteria. The applicants have proposed a method of producing high purity nitrogen dioxide gas, and an apparatus for storing the nitrogen dioxide gas thus produced by this method in Patent Document 2.
The sterilization apparatus of Patent Document 2 achieves high sterilization effect by the use of nitrogen dioxide gas. This sterilization apparatus, however, is directed to sterilization of medical tools or food package materials as the objects of sterilization. Therefore, after the objects are accommodated in the processing chamber and a substantial vacuum is drawn in the chamber, the chamber is filled with nitrogen dioxide gas to a concentration as high as several tens of thousands ppm. The sterilization apparatus can thus sterilize even small parts such as inside of tubes in a short time.
Meanwhile, there are needs for other sterilization applications that do not require such a high degree of sterilization, but require uniform sterilization of a wide space with people in it such as a clean room as the object of sterilization, with a safe, low concentration of nitrogen dioxide gas, even though it may take a long time. There are other operations other than sterilization such as disinfection or decontamination for reducing microorganisms, but these will herein all be inclusively called “sterilization”.
Patent Document 1: Japanese Patent Application Laid-open No. S58-162276
Patent Document 2: Japanese Patent Application Laid-open No. 2010-202448